I've researched bugs on this quest and have not resolved the inability to access the location of Shalidor's writings when directed to Wolfskull Cave. I had completed the "The Man Who Cried Wolf" quest before I began the Shalidor's Writings quest, although I do not recall which of the two quests I received first.
Does the order I received the quests matter? More importantly, is there a way to fix this quest so I can retrieve the writings and complete the quest?
If it helps, I'm playing the PC version.
Best Answer
If you're on PC, try this command
setstage MGR21 20, the game should act like you have collected the item. If you're not on PC, there isn't anything you can do, but at least this quest isn't very important.